Plate LI 



Figs. 32 and ^s. Frontal sections of a 1.3 millimeter embrj'o. Columbia 

 Collection, No. 167, at the levels indicated in the preceding figure 

 showing tears in the periderm of the orbital inclusion causing it to re- 

 semble an open fold, X 300, reduced to f. 



la. Secondary buccal sulcus. 

 S. Orbital inclusion, pars cylindrica. 

 II. Separating sulci. 



